1 What are the basic ingredients in concrete 2 What is the d

1. What are the basic ingredients in concrete? 2. What is the difference between density (solid density) with bulk density? . Define initial set and final set. Briefly discuss one method used to determine them . What is a false set and flash set of portland cement? 5. What is meant by air-entraining?

Solution

1) The basic ingredients in concrete are cement,coarse aggregates,fine aggregates and water. There are also admixtures added to obtain desired properties of concrete

2)solid density is the density of the the substance which is basically the weight per unit volume the substance would have if there was inter paticle void .Buld density is the weight of substance per unit volume,if the volume also includes inter particle air voids.

Solid density is a material property,whereas bulk density is not.

3) initial setting is the phenomenon where the cement starts hardening or starts gaining strength. Final setting is the time when the cement has lost its plasticity

The initial and final setting time of cement can be measured using Vicat apparatus

4)False set occurs because some of the gypsum dehydrates as a result of contacting hot clinker or high temperatures in the grinding mill. This creates plaster that rehydrates to form gypsum and stiffen the concrete.

If inadequate amounts of gypsum are added to the cement, flash set can occur--a rapid development of rigidity in freshly mixed portland cement paste, mortar, or concrete. Further mixing can\'t dispel this rigidity, and a large amount of heat is produced in the process.